A time synchronization method under satellite denial conditions

Abstract

The present invention provides a time synchronization method under satellite denial conditions, comprising: using time division multiple access to collaboratively network multiple nodes; periodically inserting bidirectional frame synchronization time slots into the communication time slots between the master node and the subnodes; utilizing each subnode to perform collision synchronization with the master node in the bidirectional frame synchronization time slots to achieve time synchronization with the master node; obtaining clock error observations of each subnode in each bidirectional frame synchronization time slot, performing Kalman filtering using the clock error observations to obtain crystal oscillator errors of each subnode, and correcting the time synchronization errors of each subnode using the crystal oscillator errors; and dynamically adjusting the period of inserting bidirectional frame synchronization time slots using observability joint decision conditions. The technical solution of the present invention solves the technical problem in the prior art that only the accuracy of time synchronization can be guaranteed at the moment of time synchronization, but the accuracy between two adjacent time synchronizations cannot be guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of radio communication technology, and in particular to a time synchronization method under satellite denial conditions. Background Art

[0002] High-precision time synchronization is a crucial prerequisite and foundation for coordinated detection, precise command and control, and combat coordination. Satellite-based positioning and timing are crucial for achieving precise spatiotemporal synchronization within swarm formations. However, traditional satellite navigation systems suffer from weak signals and the risk of interference in complex electromagnetic countermeasure environments, making them unable to provide reliable spatiotemporal synchronization information. Therefore, to meet the system's high-precision time synchronization requirements, data links are required for time synchronization under satellite-denied conditions. Data link systems utilize waveforms designed with appropriate source coding, channel coding, modulation and demodulation, and antenna technologies to achieve point-to-point transmission within wireless channels. Furthermore, data link systems employ various techniques, such as direct sequence spread spectrum, frequency hopping, and time hopping, to enhance their anti-interference and anti-destruction capabilities, improving their adaptability in complex electromagnetic environments. Furthermore, data link networking enables coordinated, conflict-free, and reliable communication among multiple data link platforms, ensuring on-demand transmission of services from different platforms within the data link network.

[0003] However, time synchronization requires that the frequency and phase of the slave node clocks match those of the master node. Frequency differences between the clocks affect ranging accuracy and, over time, accumulate as phase deviation, which in turn affects time synchronization accuracy. Existing methods for time synchronization using data links do not account for the frequency error of crystal oscillators, ensuring only the required accuracy at the moment of time synchronization, but not between synchronization moments. Summary of the Invention

[0004] The present invention provides a time synchronization method under satellite denial conditions, which can solve the technical problem in the prior art that the accuracy of the time synchronization moment can only be guaranteed but the accuracy between two adjacent time synchronizations cannot be guaranteed.

[0005] According to one aspect of the present invention, a time synchronization method under satellite denial conditions is provided, the time synchronization method comprising:

[0006] Use time division multiple access to coordinate networking of multiple nodes, and designate any one of the multiple nodes as the master node, and the remaining nodes as sub-nodes;

[0007] Periodically inserting a bidirectional frame synchronization time slot into the communication time slot between the master node and the sub-node;

[0008] Each sub-node is used to perform collision synchronization with the master node in the two-way frame synchronization time slot to complete time synchronization with the master node;

[0009] Obtain the clock error observation of each sub-node in each bidirectional frame synchronization time slot, use the clock error observation to perform Kalman filtering to obtain the crystal oscillator error of each sub-node, and use the crystal oscillator error to correct the time synchronization error of each sub-node;

[0010] An observability joint decision condition is established, and the period of inserting bidirectional frame synchronization time slots is dynamically adjusted using the observability joint decision condition.

[0011] Furthermore, the bidirectional frame synchronization time slot includes a frame alignment start time slot, a frame alignment feedback time slot and a frame alignment error broadcast time slot.

[0012] Furthermore, utilizing each sub-node to perform collision synchronization with the master node in a bidirectional frame synchronization time slot to perform time synchronization with the master node includes:

[0013] In the frame alignment start time slot, the master node sends a frame alignment data packet to each sub-node. The frame header of the frame alignment data packet contains the local time of the master node.

[0014] Each child node calculates the local time difference between its own local time and the master node local time contained in the frame alignment data packet based on the received frame alignment data packet, and uses the local time difference value to make an initial correction to the local time of each child node;

[0015] In the frame alignment feedback time slot, each sub-node sends its own frame alignment feedback data packet to the master node. The frame alignment feedback data packet contains the local time of the corresponding sub-node after the initial correction.

[0016] The master node calculates the frame alignment error between itself and each sub-node based on the frame alignment feedback data packets received from each sub-node.

[0017] In the frame alignment error broadcast time slot, the master node broadcasts the calculated frame alignment error of each child node;

[0018] Each child node performs a secondary correction on its own local time according to the received frame alignment error.

[0019] Furthermore, the master node calculates the frame alignment error between itself and each child node based on the frame alignment feedback data packets received from each child node using the following formula:

[0020]

[0021] In the above formula, represents the frame alignment error between the master node and child node j, It represents the local time in the master node when the master node receives the frame alignment feedback data packet from child node j. Indicates the first corrected local time contained in the frame alignment feedback packet of child node j received by the master node.

[0022] Furthermore, the joint decision condition for observability is:

[0023]

[0024] In the above formula, M represents the number of bidirectional frame synchronization time slots, represents the relative time divergence of child node j in the i-th bidirectional frame synchronization time slot, represents the frame alignment error between the master node and child node j in the i-th bidirectional frame synchronization time slot, represents the local time difference between the master node and the child node j in the i-th bidirectional frame synchronization time slot, P represents the covariance matrix of the Kalman filter constructed based on the clock difference model, D1 represents the first preset threshold value, D2 represents the second preset threshold value, and D3 represents the third preset threshold value.

[0025] Furthermore, dynamically adjusting the period of inserting the bidirectional frame synchronization time slot using the observability joint decision condition includes: determining whether the observability joint decision condition is met, if so, extending the period of the bidirectional frame synchronization time slot; if not, shortening the period of the bidirectional frame synchronization time slot.

[0026] Furthermore, the crystal oscillator error includes the phase error, and the phase error model is:

[0027]

[0028] In the above formula, x(T) represents the phase of the crystal oscillator relative to the starting time, x0 represents the initial phase deviation, y0 represents the initial frequency deviation, T represents the period of the two-way frame synchronization time slot, a represents the frequency drift rate, and n(T) represents the random error of the crystal oscillator.

[0029] Furthermore, random errors include phase white noise, phase flicker noise, frequency white noise, frequency flicker noise and frequency random walk noise.

[0030] The technical solution of the present invention is applied to provide a time synchronization method under satellite denial conditions. The method is networked in a time division multiple access manner to connect multiple nodes. By periodically inserting two-way frame synchronization time slots in the communication time slots of the master node and the sub-nodes, high-precision time synchronization of the two-way frame synchronization time slots is achieved by utilizing collision synchronization between the master node and each sub-node. At the same time, Kalman filtering is performed using clock difference observations to filter and estimate crystal oscillator errors, thereby suppressing the influence of crystal oscillator frequency drift on time synchronization accuracy. The observability joint decision condition is used to dynamically adjust the period of inserting the two-way frame synchronization time slot, thereby achieving high-precision time synchronization between the two-way frame synchronization time slots. While ensuring the time synchronization accuracy, the occupancy of the communication bandwidth is reduced, thereby reducing the influence of time synchronization on the communication rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the embodiments of the present invention, constitute a part of the specification, illustrate the embodiments of the present invention, and together with the description, explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0032] Figure 1 A schematic diagram of a collaborative networking strategy for a time synchronization method under satellite denial conditions provided according to a specific embodiment of the present invention is shown;

[0033] Figure 2 A schematic diagram of time slot division within a network provided according to a specific embodiment of the present invention is shown;

[0034] Figure 3 A schematic diagram of a collision timing process according to a specific embodiment of the present invention is shown;

[0035] Figure 4 A schematic diagram of a joint observability decision process according to a specific embodiment of the present invention is shown;

[0036] Figure 5 A schematic diagram of an elastic collision timing mechanism under observability constraints provided according to a specific embodiment of the present invention is shown. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] Unless otherwise specifically stated, the relative arrangement of the parts and steps, the numerical expressions and the numerical values ​​set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values ​​should be interpreted as being merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0040] According to a specific embodiment of the present invention, a time synchronization method under satellite denial conditions is provided, which includes: using time division multiple access to collaboratively network multiple nodes, and designating any one of the multiple nodes as a master node, and the remaining nodes as sub-nodes; periodically inserting a two-way frame synchronization time slot in the communication time slot between the master node and the sub-node; using each sub-node to perform collision synchronization with the master node in the two-way frame synchronization time slot to complete time synchronization with the master node; obtaining a clock difference observation value of each sub-node in each two-way frame synchronization time slot, using the clock difference observation value to perform Kalman filtering to obtain a crystal oscillator error of each sub-node, and using the crystal oscillator error to correct the time synchronization error of each sub-node; establishing an observability joint decision condition, and using the observability joint decision condition to dynamically adjust the period of inserting the two-way frame synchronization time slot.

[0041] This configuration method provides a time synchronization method under satellite denial conditions. The method uses time division multiple access to establish a network, connects multiple nodes, and periodically inserts two-way frame synchronization time slots into the communication time slots of the master node and sub-nodes. The collision synchronization between the master node and each sub-node is used to achieve high-precision time synchronization of the two-way frame synchronization time slots. At the same time, a Kalman filter is performed using clock difference observations to filter and estimate the crystal oscillator error, suppressing the impact of crystal oscillator frequency drift on time synchronization accuracy. The observability joint decision condition is used to dynamically adjust the period of inserting two-way frame synchronization time slots, achieving high-precision time synchronization between two-way frame synchronization time slots. While ensuring time synchronization accuracy, the occupancy of communication bandwidth is reduced, thereby reducing the impact of time synchronization on communication rate. Compared with the existing technology, the technical solution of the present invention can solve the technical problem that the existing technology can only guarantee the accuracy of time synchronization at the moment, but cannot guarantee the accuracy between two adjacent time synchronizations.

[0042] Among them, the networking strategy is as follows Figure 1As shown, the network includes N identical nodes, and time division multiple access is used to complete node access. The number of nodes can be configured according to actual conditions. In addition, in this embodiment of the present invention, the bidirectional frame synchronization time slot includes a frame alignment start time slot, a frame alignment feedback time slot, and a frame alignment error broadcast time slot. Based on this embodiment, using each child node to perform collision time alignment with the master node in a bidirectional frame synchronization time slot to synchronize time with the master node includes: in a frame alignment start time slot, the master node sends a frame alignment data packet to each child node, and the frame header of the frame alignment data packet contains the local time of the master node; each child node calculates the local time difference between its own local time and the local time of the master node contained in the frame alignment data packet based on the received frame alignment data packet, and uses the local time difference value to perform an initial correction on the local time of each child node; in a frame alignment feedback time slot, each child node sends its own frame alignment feedback data packet to the master node as feedback, and the frame alignment feedback data packet contains the local time of the corresponding child node after the initial correction; the master node calculates the frame alignment error between itself and each child node based on the frame alignment feedback data packets received from each child node; in a frame alignment error broadcast time slot, the master node broadcasts the calculated frame alignment error of each child node; each child node performs a secondary correction on its own local time based on the received frame alignment error.

[0043] That is to say, in the collision timing strategy proposed by the present invention, each child node will complete two time corrections in one two-way frame synchronization time slot. In the first correction, the local time of the child node is aligned with the received master node frame header, that is, the local time of the child node is corrected to be consistent with the local time contained in the received master node frame header. The adjustment amount, that is, the local time difference value, is recorded as ; The second time, each sub-node receives the frame alignment error value broadcast by the master node, which is also the data transmission delay. Correct local time. and The sum is the total correction amount completed in a collision timing, that is, the relative time divergence δT of the current timing of child node j relative to the previous timing j0 After the correction is completed, efficient and high-precision time synchronization can be achieved. By performing two corrections in a two-way frame synchronization time slot, high-precision time synchronization can be achieved between each node.

[0044] In order to have a further understanding of the process of collision timing, the following Figure 2 and Figure 3 The collision timing process is described in detail. Figure 2 and Figure 3As shown in the figure, taking node 0 as the master node and nodes 1 to (N-1) as child nodes as an example, the specific collision time synchronization process is as follows: first, in the frame alignment start time slot, only node 0 as the master node sends a frame alignment data packet containing the local time. After receiving the frame alignment data packet, the other child nodes 1 to (N-1) correct their local times to be consistent with the local time of the master node; after the correction is completed, nodes 1 to (N-1) respectively send frame alignment feedback data packets containing their local times to node 0 in their respective time slots. After receiving the data packets from each child node, node 0 calculates the data transmission delay between each child node and the master node, that is, the frame alignment error; then, in the frame alignment error broadcast time slot, node 0 broadcasts the frame alignment error calculated previously between itself and each child node. After receiving the frame alignment error, nodes 1 to (N-1) perform a second correction on their local times, completing high-precision time synchronization between nodes.

[0045] Furthermore, in an embodiment of the present invention, the master node calculates the frame alignment error between itself and each child node based on the frame alignment feedback data packets received from each child node using the following formula:

[0046]

[0047] In the above formula, represents the frame alignment error between the master node and child node j, It represents the local time in the master node when the master node receives the frame alignment feedback data packet from child node j. Indicates the first corrected local time contained in the frame alignment feedback packet of child node j received by the master node.

[0048] After the above-mentioned time synchronization is completed, each child node keeps time through the local clock module. However, due to the influence of the node's own crystal oscillator performance, in actual applications, the accuracy of time synchronization between the child node and the master node will diverge due to changes in the crystal oscillator frequency error, resulting in the gradual accumulation of time synchronization errors between nodes over time.

[0049] In order to eliminate the crystal oscillator error of each child node, the present invention proposes a flexible cooperative clock taming technology based on convergence judgment. Specifically, the clock difference is used as the observation quantity, and the crystal oscillator error, that is, the phase error, is used as the state vector. The phase error is filtered and estimated by Kalman filtering, and the phase error obtained by filtering estimation is used in real time to correct each child node, thereby eliminating the time synchronization error caused by the crystal oscillator error. At the same time, the observability joint judgment condition is used to dynamically adjust the period of inserting the bidirectional frame synchronization time slot to ensure the time synchronization accuracy while reducing the impact on the communication bandwidth.

[0050] In the embodiment of the present invention, the crystal oscillator error includes a phase error, and the model of the phase error is:

[0051]

[0052] In the above formula, x(T) represents the phase of the crystal oscillator relative to the starting time, x0 represents the initial phase deviation, y0 represents the initial frequency deviation, T represents the period of the two-way frame synchronization time slot, a represents the frequency drift rate, and n(T) represents the random error of the crystal oscillator. Specifically, random error includes phase white noise, phase flicker noise, frequency white noise, frequency flicker noise, and frequency random walk noise.

[0053] Furthermore, in an embodiment of the present invention, the observability joint decision condition dynamically adjusts the period of inserting the bidirectional frame synchronization time slot, including: determining whether the observability joint decision condition is met, and if so, extending the period of the bidirectional frame synchronization time slot; if not, shortening the period of the bidirectional frame synchronization time slot. In this way, the impact on the communication bandwidth can be reduced while ensuring the accuracy of time synchronization, thereby reducing the impact on the communication rate. Specifically, in an embodiment of the present invention, the observability joint decision condition is:

[0054]

[0055] In the above formula, M represents the number of bidirectional frame synchronization time slots, δT j0 (i) represents the relative time divergence of child node j in the i-th bidirectional frame synchronization time slot, represents the frame alignment error between the master node and child node j in the i-th bidirectional frame synchronization time slot, represents the local time difference between the master node and child node j in the i-th bidirectional frame synchronization time slot, P represents the covariance matrix of the Kalman filter constructed based on the clock error model, D1 represents the first preset threshold value, D2 represents the second preset threshold value, and D3 represents the third preset threshold value. The specific values ​​of D1, D2, and D3 are determined according to actual conditions.

[0056] In order to further understand the flexible cooperative clock taming process based on convergence judgment of the present invention, the following Figure 4 and Figure 5 For detailed description. Figure 4 As shown in , in the initial stage, the two-way frame synchronization time slot interval is made small, that is, a large number of clock error observations are quickly acquired at a high time synchronization frequency, and after filtering the clock error observations, a joint decision on the observability of the estimation results is made. Figure 5As shown, the interval of the two-way frame synchronization slots, that is, the period of the two-way frame synchronization slots, is dynamically adjusted based on the results of the joint observability decision. If the observability decision condition is met, indicating that the error estimation result meets the requirements for high-precision time maintenance, the time synchronization slot interval (that is, the period of the two-way frame synchronization slots) can be extended, entering a sparse observation state to reduce the impact of the time synchronization slots on the communication bandwidth. Otherwise, the period of the two-way frame synchronization slots is shortened to ensure the accuracy of time synchronization. This dynamic adjustment enables flexible coordinated clock training of each node, ensuring that the two-way frame synchronization slots and every moment between time slots meet the requirements of high-precision time synchronization.

[0057] In summary, the present invention provides a time synchronization method under satellite denial conditions. The method is networked in a time division multiple access manner, multiple nodes are connected, and high-precision time synchronization of the two-way frame synchronization time slots is achieved by periodically inserting two-way frame synchronization time slots in the communication time slots of the master node and the sub-nodes, and using the collision synchronization between the master node and each sub-node. At the same time, Kalman filtering is performed using clock difference observations to filter and estimate the crystal oscillator error, suppressing the influence of crystal oscillator frequency drift on the time synchronization accuracy, and dynamically adjusting the period of inserting two-way frame synchronization time slots using observability joint decision conditions to achieve high-precision time synchronization between two-way frame synchronization time slots. While ensuring the accuracy of time synchronization, the occupancy of communication bandwidth is reduced, thereby reducing the impact of time synchronization on the communication rate. Compared with the prior art, the technical solution of the present invention can solve the technical problem that the prior art can only guarantee the accuracy of the time synchronization moment but cannot guarantee the accuracy between two adjacent time synchronizations.

[0058] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0059] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0060] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A time synchronization method under satellite denial conditions, characterized in that: The time synchronization method comprises: A time division multiple access method is used to coordinate networking of multiple nodes, and any one of the multiple nodes is designated as a master node, and the remaining nodes are child nodes; Periodically inserting a bidirectional frame synchronization time slot into the communication time slot between the master node and the sub-node; Using each sub-node to perform collision synchronization with the master node in the bidirectional frame synchronization time slot to complete time synchronization with the master node; Obtaining a clock error observation value of each subnode in each bidirectional frame synchronization time slot, performing Kalman filtering using the clock error observation value to obtain a crystal oscillator error of each subnode, and correcting the time synchronization error of each subnode using the crystal oscillator error; Establishing an observability joint decision condition, and dynamically adjusting a period of inserting the bidirectional frame synchronization time slot using the observability joint decision condition; The joint observability decision condition is: In the above formula, M represents the number of bidirectional frame synchronization time slots, δT j0 (i) represents the relative time divergence of child node j in the i-th bidirectional frame synchronization time slot, represents the frame alignment error between the master node and child node j in the i-th bidirectional frame synchronization time slot, represents the local time difference between the master node and the child node j in the i-th bidirectional frame synchronization time slot, P represents the covariance matrix of the Kalman filter constructed based on the clock difference model, D1 represents the first preset threshold value, D2 represents the second preset threshold value, and D3 represents the third preset threshold value.

2. The time synchronization method according to claim 1, wherein: The bidirectional frame synchronization time slots include a frame alignment start time slot, a frame alignment feedback time slot and a frame alignment error broadcast time slot.

3. The time synchronization method according to claim 2, characterized in that: Using each sub-node to perform collision timing with the master node in the bidirectional frame synchronization time slot to perform time synchronization with the master node includes: In the frame alignment start time slot, the master node sends a frame alignment data packet to each child node, wherein the frame header of the frame alignment data packet includes the local time of the master node; Each child node calculates a local time difference between its own local time and the master node local time contained in the frame alignment data packet according to the received frame alignment data packet, and uses the local time difference value to perform an initial correction on the local time of each child node; In the frame alignment feedback time slot, each child node sends a frame alignment feedback data packet to the master node, where the frame alignment feedback data packet includes the initially corrected local time of the corresponding child node; The master node calculates the frame alignment error between the master node and each sub-node according to the received frame alignment feedback data packets of each sub-node; In the frame alignment error broadcasting time slot, the master node broadcasts the calculated frame alignment error of each child node; Each child node performs a secondary correction on its own local time according to the received frame alignment error.

4. The time synchronization method according to claim 3, characterized in that: The master node calculates the frame alignment error between itself and each sub-node based on the frame alignment feedback data packets received from each sub-node using the following formula: In the above formula, represents the frame alignment error between the master node and child node j, It represents the local time in the master node when the master node receives the frame alignment feedback data packet from child node j. Indicates the first corrected local time contained in the frame alignment feedback packet of child node j received by the master node.

5. The time synchronization method according to claim 4, characterized in that: Dynamically adjusting the period of inserting the bidirectional frame synchronization time slot using the observability joint decision condition includes: judging whether the observability joint decision condition is met, if so, extending the period of the bidirectional frame synchronization time slot; if not, shortening the period of the bidirectional frame synchronization time slot.

6. The time synchronization method according to claim 5, characterized in that: The crystal oscillator error includes a phase error, and the model of the phase error is: In the above formula, x(T) represents the phase of the crystal oscillator relative to the starting time, x0 represents the initial phase deviation, y0 represents the initial frequency deviation, T represents the period of the two-way frame synchronization time slot, a represents the frequency drift rate, and n(T) represents the random error of the crystal oscillator.

7. The time synchronization method according to claim 6, characterized in that: The random errors include phase white noise, phase flicker noise, frequency white noise, frequency flicker noise and frequency random walk noise.

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